On 10/21/2017 09:23 PM, Jonathan Cameron wrote:
> On Sat, 21 Oct 2017 18:54:01 +0100
> Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
>
>> On Tue, 17 Oct 2017 15:15:43 +0200
>> Fabrice Gasnier <fabrice.gasnier@xxxxxx> wrote:
>>
>>> STM32H7 ADC channels may be configured either as single-ended or
>>> differential.
>>> Add 'st,adc-diff-channels' property to support differential channels.
>>> Differential channels are defined as a pair of positive and negative
>>> inputs: vinp & vinn.
>>>
>>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
>> Hmm. Fair enough. Sometimes we support both types of channels
>> and leave it to userspace, but in many cases that makes little sense
>> - particularly if like I think is going on here, we aren't combining channels
>> that can be separately read but rather the negative pin is simply unused
>> when we are in single channel mode... (did I understand that right?)
> I clearly didn't understand. This is same as other devices
> in that we are picking a pair from the channels that can otherwise be
> used as single end channels. (I think).
Hi Jonathan,
Indeed, we're picking a pair from the channels that can be used as
single channels otherwise.
Also, it doesn't makes sense to leave the choice to userspace: when
these channels are used in differential mode, both input should be
biased. This is quite dependent on hardware (board), not really a
runtime choice.
Hope this clarifies ?
>
> For this binding I think I'd like to see an example added showing how
> this works...
You're right, I should have added that. Please let me know if I can add
bellow example in v2:
Example to setup differential channels 1, 2 & 3 (with resp. 0, 6 & 7
negative inputs):
adc: adc@40022000 {
compatible = "st,stm32h7-adc-core";
...
adc1: adc@0 {
compatible = "st,stm32h7-adc";
...
st,adc-diff-channels = <1 0>, <2 6>, <3 7>;
};
};
Thanks for reviewing,
Best Regards,
Fabrice
>
> Thanks,
>
> Jonathan
>>
>> Jonathan
>>
>>> ---
>>> Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt | 6 ++++++
>>> 1 file changed, 6 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt b/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
>>> index 48bfcaa3..c3c8de1 100644
>>> --- a/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
>>> +++ b/Documentation/devicetree/bindings/iio/adc/st,stm32-adc.txt
>>> @@ -62,6 +62,12 @@ Required properties:
>>> - st,adc-channels: List of single-ended channels muxed for this ADC.
>>> It can have up to 16 channels on stm32f4 or 20 channels on stm32h7, numbered
>>> from 0 to 15 or 19 (resp. for in0..in15 or in0..in19).
>>> +- st,adc-diff-channels: List of differential channels muxed for this ADC.
>>> + Depending on part used, some channels can be configured as differential
>>> + instead of single-ended (e.g. stm32h7). List here positive and negative
>>> + inputs pairs as <vinp vinn>, <vinp vinn>,... vinp and vinn are numbered
>>> + from 0 to 19 on stm32h7)
>>> + Note: At least one of "st,adc-channels" or "st,adc-diff-channels" is required.
>>> - #io-channel-cells = <1>: See the IIO bindings section "IIO consumers" in
>>> Documentation/devicetree/bindings/iio/iio-bindings.txt
>>>
>>
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